Define best. Squeeze is most tested and everything(tm) seems to be working as advertised. Unless it's too outdated to work for your needs, that is. Wheezy is most up-to-date with some irritating (albeit, limited to only few programs, namely GIMP, chromium, and gparted, as discovered to date) problems.

While I really, really appreciate sulu's heroic attempts to get Jessie working, even via his own words it sounds like "avoid touching with a long stick" - it doesn't fix any of Wheezy problems, and have probability of creating new ones, not to mention being royal pita to update. Sounds like an option only, if you're really desperate for some Jessie-dependant version/program.

/Estel